A Mercedes Benz S280 with a mileage of about 143000 km. When the vehicle speed is below 100km / h, the acceleration is normal; when the vehicle speed is above 100km / h, the acceleration is weak, and the engine warning light gives an alarm. Engine idle jitter in place, turn off the ignition switch and start again, engine idle jitter disappears.

故障診斷：啟動發動機觀察運轉情況，怠速轉速750r/min無抖動，加速到2000r/min無抖動，加速到3500r/min無抖動。在高速公路上試車，車速在100km/h以下加速有力，車速在100km/h以上加速坐車，停車后出現發動機怠速抖動。

No engine speed jitter was detected at 20 000 R / 750 min, no engine speed jitter was detected during acceleration. In the test run on the highway, when the speed is below 100km / h, the acceleration is powerful, when the speed is above 100km / h, the engine idling jitter occurs after parking.

用診斷儀檢測存儲當前故障碼“3缸、6缸失火”，讀取實際值“3缸、6缸失火超過失火限值”，已不能點火，讀取噴油時間為3.6～3.8ms，標準為2.7～4.2msa

Use the diagnostic instrument to detect and store the current fault code "misfire of cylinder 3 and 6", read the actual value "misfire of cylinder 3 and 6 exceeds the misfire limit", and the ignition can not be started. The read injection time is 3.6 ~ 3.8ms, and the standard is 2.7 ~ 4.2msa

拆卸3缸、6缸點火線圈檢查未發現異常，拆卸火花塞檢查發現電極間隙較大。測量所有汽缸壓力均為1100kPa，符合要求。測量發動機控制模塊到3缸、6缸點火線圈的導線電阻為0.2Ω，符合要求。更換全部火花塞，將3缸、6缸點火線圈與2缸、5缸互換，路試故障現象依舊，故障碼仍是“3缸、6缸失火”。

No abnormality was found after the ignition coils of cylinder 3 and 6 were disassembled, and large electrode gap was found after the spark plug was disassembled. All cylinder pressures measured are 1100kpa, meeting the requirements. The wire resistance from the engine control module to the ignition coil of cylinder 3 and 6 is 0.2 Ω, which meets the requirements. All spark plugs were replaced, and the ignition coils of cylinder 3 and 6 were exchanged with those of cylinder 2 and 5. The road test showed that the fault still existed, and the fault code was still "cylinder 3 and 6 are on fire".

測量燃油壓力，怠速為380kPa、急加速時壓力降至340kPa，然后迅速提升到420kPa。拆開三元催化器連接處，用內窺鏡觀察蜂窩狀陶瓷載體透氣良好。

The fuel pressure is measured. The idle speed is 380kpa, the pressure drops to 340kpa during rapid acceleration, and then rises to 420kpa rapidly. The connection of the three-way catalytic converter was disassembled, and the honeycomb ceramic carrier was observed by endoscope.

清洗節氣門、噴油器，路試加速性能有好轉，但加速性能仍不正常，高速行駛停車后發動機出現抖動，故障碼只是“6缸失火”。將6缸與2缸的噴油器互換，路試仍是高速加速無力，故障碼仍是“6缸失火”。

After cleaning the throttle and fuel injector, the acceleration performance of the road test is improved, but the acceleration performance is still abnormal. The engine shakes after parking at high speed, and the fault code is "cylinder 6 misfire". If the injector of cylinder 6 and cylinder 2 are interchanged, the high-speed acceleration is still weak in the road test, and the fault code is still "cylinder 6 misfire".

通過多次試車，該車低速加速動力正常，高速加速明顯無力，懷疑燃油泵工作不正常。做燃油泵供油量測試，運轉40s泵油1L，達到標準值的下限。對正常車輛做燃油泵供油量測試，測試結果高出1L很多。

After many tests, the low-speed acceleration power of the car is normal, and the high-speed acceleration is obviously weak. It is suspected that the fuel pump is not working properly. Test the fuel supply quantity of the fuel pump, run for 40s, Pump Oil 1L, reach the lower limit of the standard value. The test result of fuel supply quantity of normal vehicle is much higher than 1L.

故障排除：更換燃油泵，接上燃油壓力表，觀察原地加速時燃油壓力沒有下降現象。試車，高速加速性能正常，故障排除。

Troubleshooting: replace the fuel pump, connect the fuel pressure gauge, and observe that the fuel pressure does not drop when accelerating in situ. Test run, high speed acceleration performance is normal, troubleshooting.

故障總結：此車為軟故障，測量此車燃油壓力為標準值的下極限，如果不與正常車輛數據對比察覺不出異常，通過對比找到軟故障的原因所在。

Fault summary: this car is a soft fault. The fuel pressure of this car is measured as the lower limit of the standard value. If there is no abnormality detected by not comparing with the normal vehicle data, the cause of the soft fault can be found through comparison.